Synthetic ester lubricants containing antioxidants



United States Patent 3,288,7l3 Patented Nov. 29, 1966 fice This invention relates to ester-based lubricant compositions containing a novel combination of base oilsoluble additive agents. More particularly, the present invention relates to ester-based synthetic lubricant compositions which exhibit increased oxidation resistance.

Organic compounds, such as lubricating oils, undergo oxidation upon exposure to air. This process is accentuated by elevated temperatures such as occur in engines and other operating machinery. When such organic compositions are used as motor or machinery lubricants, their stability is still further drastically reduced due to their contact with metal surfaces which give up metallic particles to the lubricant. Such abraded or dissolved metals or metal salts appear to act as oxidation catalysts in the lubricant causing the formation of primary oxidation products which in turn cause further degradation of the organic compounds present in the composition. In addition, water also causes corrosion of metallic surfaces and accentuates oxidation of the lubricant.

Problems of this nature are encountered in mineral oils but appear to be particularly troublesome in synthetic oleaginous fluids exemplified by esters. Ordinarily, these synthetic ester fluids can be effectively inhibited against oxidation by the use of small amounts of additives. However, in the presence of certain metals and metal compounds often occurring in the lubricants, particularly as aforementioned, through contact with metal surfaces such as iron, the effectiveness of the additives is greatly reduced.

The present invention provides a synthetic ester-based lubricant containing a primary antioxidant and certain N-substituted amino compounds. The N-substituted amino compounds of the invention can be represented by the following general formula:

wherein X is a pyridyl or quinolyl radical and can be substituted as with straight or branched chain alkyl groups of l to 12 carbon atoms, perferably 1 to 8 carbon atoms, or with other non-interfering substituents such as hydroxy or alkoxy groups; and is an n-va1ent hydrocarbon radical of up to 16 or even, 20, 24 or more carbon atoms whose adjacent carbon atoms are no closer than 1.40 A., (i.e., a non-olefinic, non-acetylenic hydrocarbon. Thus R may be an aromatic hydrocarbon radical-containing n-valent hydrocarbon radical. R can be an aryl or mixed aryl-alkyl radical. R can also be substituted with non-interfering groups such as hydroxyl, alkyl and alkoxyl groups. R is often phenyl, including substituted phenyl, phenyl-substituted lower alkyl or a mixed phenyllower alkyl radical. The integer n is a value of 1 to 2.

Examples of preferred groups of N-substituted amino compounds contemplated by the present invention are:

A. N-substituted aminopyridine represented by the structural formula:

wherein R is hydrogen or an alkyl group of 1 to 12 carbon atoms, perferably l to 8 carbon atoms, and R is a hydrocarbyl, aryl or alkyl group of 1 to 12 carbon atoms;

B. N-substituted aminoquinoline having the structural formula:

R NHR:

wherein R and R are as defined in A above and R and NHR are on different carbon atoms of positions 2 to 8.

.C. The condensation product of aldehyde and aminopyridines having the structural formula:

t R3 R1 ii R1 H wherein R is as identified in A above and R is an alkyl group of 1 to 12, preferably 1 to 8 carbon atoms. Any process known in the art for the production of these products can be employed as, for example, heating to reaction temperature, usually about to C., at least 2 moles of the aminopyridine with 1 mole of an aldehyde of l to 12 carbon atoms, perferably in the presence of an azeotroping solvent such as toluene.

D. The condensation product of aminopyridine, aldehyde and alkylphenol having the structural formula:

wherein R is as defined in A above; R is a divalent alkyl radical of 1 to 4 carbon atoms and R is an alkyl group of 1 to 8 carbon atoms, preferably a tertiary .alkyl radical located in a position para to the hydroxy substituents, for instance as in These compounds like those of C above can be prepared by known condensation methods, for instance, by reacting together 2 moles of an aminopyridine, 2 moles of an aldehyde of 1 to 4 carbon atoms and 1 mole of an alkylphenol in the presence of an azeotroping solvent for water.

The primary antioxidant component of the invention is an aromatic amine which is soluble in the ester fiuid to extent used and can be represented by the following general formula:

wherein Q is a monovalent hydrocarbon of 1 to 20 carbons, preferably 6 to 12 carbon atoms, whose adjacent carbon atoms are no closer than 1.40 A., (i.e., a nonolefinic, non-acetylenic, monovalent hydrocarbon), and Q is an aromatic hydrocarbon radical of 6 to 12 or 16 carbon atoms. Thus Q can be an alkyl group, including cycloalkyl, or an aromatic group. Preferably, both Q and Q are aromatic and often at least one is a fused ring aromatic, e.g., naphthyl. Q and Q can be substituted with non-interfering substituents such as alkyl groups and amine groups, preferably alkyl or aromatic amines, and Q and Q can be linked together by means of a noninterfering element such as carbon, sulfur and oxygen.

Illustrative of suitable amines are phenothi-azine, N- phenyl-a-naphthyl amine; di(ix-naphthyl amine); N-N- diphenyl paraphenylene diamine; N,N-dioctyl paraphenylene diamine, N,N heptylphenyl-para-phenylene diamine; diphenyl amine, N butyl phenyl-(a-decyl) amine, etc.

The additives of the present invention are used in minor amounts sufficient to retard oxidation of the synthetic lubricant at temperatures in excess of 400 F. The actual amount of the additives employed may depend upon the particular lubricant utilized and the particular N-substituted amino compound selected. Ordinarily about 0.1 to 5% by weight, more often about .1 to 1.5% by weight, of each inhibit-or based on the final composition is employed.

The lubricant composition of this invention includes as the major component a base oil which is an ester of lubricating viscosity which may be, for instance, a simple ester or compounds having multiple ester groupings, such as complex esters, polyesters or diesters. These esters are made from monoand polyhydroxy alkanols and alkane carboxylic acids, frequently of about 4 to 12 carbon atoms.

The reaction product of a monohydroxy alcohol and a monocarboxylic acid is usually considered to be a simple ester. A diester is usually considered to be the reaction product of 1 mole of a dicarboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of a monohydric alcohol or 1 mole of a glycol of 4 to 10 carbon atoms with two moles of a monocarboxylic acid of 4 to 10 carbon atoms. The diesters frequently contain from 20 to 40 carbon atoms. One complex ester is of the type in which X represents a monohydric alcohol residue, Y represents a dicarboxylic acid residue and Z represents a glycol residue and the linkages are ester linkages. Those esters, wherein X represents a monoacid residue, Y represents a glycol residue and Z represents a dibasic acid residue are also considered to be complex esters. The complex esters often have 30 to 50 carbon atoms. P0ly esters, or polyester bright stocks can be prepared by direct esterification of dibasic acids with glycols in about equimolar quantities. The polyesterification reaction is usually continued until the product has a kinematic viscosity from about to 200 centistokes at 210 R, and preferably 40 to 130 centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, they are also useful when added or blended with each other in synthetic lubricant compositions. These esters and blends have been found to be especially adaptable to the conditions to which turbine engines are exposed, since they can be formulated to give a desirable combination of high flash point, low pour point, and high viscosity at elevated temperatures. In addition, many complex esters have shown good stability to shear. There may also be included in the blends up to about 1% or more by weight of a foam inhibitor such as a methyl silicone polymer or other additives to provide a particular characteristic, for instance, extreme pressure or load carrying agents, corrosion inhibitors, etc.

Typical synthetic lubricants may be formulated essentially from a major amountabout 60 to 85%of a complex ester and a minor amountabout 15 to 40% of a diester, by stirring together a quantity of diester and complex ester at an elevated temperature, altering the proportions of each component until the desired viscosity is reached. Polyesters can be employed to thicken diester base stocks to increase the load carrying capacity of the base diester oil. The polyester will generally not comprise more than about 50 weight percent of the blend, preferably about to 35 weight percent. Usually the Other polymers such as Acryloids may be added as thickeners to the esters, generally the simple esters such as the above diesters, to obtain a base oil of desired viscosity. The Acryloids are polymers of mixed C to C esters of methacrylic acid having 10,000 to 20,000 molecular weight. Advantageously, the final lubricating oil composition would have a maximum viscosity at -40 F. of about 13,000 centistokes and a minimum viscosity of about 3.5 centistokes at 210 F.

The monohydric alcohols employed in these esters usually contain less than about 20 carbon atoms and are generally aliphatic. Preferably, the alcohol contains up to about 12 carbon atoms. Useful aliphatic alcohols include butyl, hexyl, methyl, iso-octyl and dodecyl a1- cohols, C oxo alcohols and octadecyl alcohols. C to C branched chain primary alcohols are frequently used to improve the low temperature viscosity of the finished lubricant composition. Alcohols such as n-decanol, 2- ethylhexanol, oxo alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products such as diisobutylene and C olefins, ether alcohols such as butyl carbitol, tripropylene glycol mono-isopropyl ether, dipropylene glycol mono-isopropyl ether, and products such as Tergitol 3A3, has the formula. C13H270(CH2CI'I20)3H, are suitable alcohols for use to produce the desired lubricant. Iso-octanol and iso-decanol are alcohol mixtures made by the 0x0 process from C to C copolymer heptenes. The cut which makes up iso-octanol usually contains about 17% 3,4-dimethylhexanol; 29% 3,5-dimethylhexanol; 25% 4,5dimethylhexanol; 1.4% 5,5-dimethylhexanol; 16% of a mixture of 3-methylheptanol and S-ethylheptanol; 2.3% 4-ethylhexanol; 4.3% walkyl alkanols and 5% other materials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however, if desired they could contain a greater number. Among the specific glycols which can be employed are 2-ethyl-1,3-hexanediol, 2-propyl-3,3- heptanediol, Z-methyl-1,3pentanediol, 2-butyl-1,3-but-anediol, 2,4-diphenyl-1,3-butanediol, and 2,4-dimesityl- 1,3-butanediol. In addition to these glycols, other. glycols may be used, for instance, where the alkylene radical contains 2 to 4 carbon atoms such as diethylene glycol, dipropylene glycol and other glycols up to 1,000 to 2,000 molecular weight. The most popular glycols for the manufacture of ester lubricants appear to be polypro pylene glycols having a molecular weight of about to 300 and 2-ethyl hexanediol. The 2,2-dimethy1 glycols,

such as neopentyl glycol have been shown to impart heat stability to the final blends. Minor amounts of other glycols or other materials can be present as long as the desired properties of the product are not unduly deleteriously affected.

Aside from glycols, the esters may be made from polyhydric alcohols of more than two hydroxyl groups, eg triand tetrahydroxy aliphatic alcohols having about 4 to 12 carbon atoms, preferably about 5 to 8 carbon atoms; for instance, pentaerythritol, trimethylolpropane and the like. Particularly suitable ester base oils are formed when these alcohols are reacted with monocarboxylic acids having about 4 to 12 carbon atoms, preferably 4 to 9 carbon atoms. It is preferred that the reaction be conducted so as to substantially completely esterify the acids.

One group of alkanoic acids includes those of 6 to 24 carbon atoms such as stearic, lauric, etc. The carboxylic acids employed in making ester lubricants will often contain from about 4 to 12 carbon atoms. Suitable acids are described in US. Patent No. 2,575,195 and include the aliphatic dibasic acids of branched or straight chain structures Which are saturated or unsaturated. The preferred acids are the saturated aliphatic carboxylic acids containing not more than about 12 carbon atoms, the mixtures of these acids. Such acids include succinic, adipic, suberic, azelaic and sebacic acids and isosebacic acid which is a mixture of ot-ethyl suberic acids, ot-(llethyl adipic acid and sebacic acid. This composite of acids is attractive from the viewpoint of economy and availability since it is made from petroleum hydrocarbons rather than the natural oils and fats which are used in the manufacture of many other dicarboxylic acids, which natural oils and fats are frequently in short supply. The

6 usually at least about 140 C. but not so high as to decompose the wanted product. The highest temperature needed for the reaction will probably be about 200 C., preferably not over about 175 C. The pressure is conpreferred dibasic acids are sebacic and azelaic or mix- 5 venifinfly p Although hh P F tures thereof. Minor amounts of adipic used with a Superahhosphenc Pressure Could he IltlhZed, there 15 major amount of sebacic may also be used with advantage. usually no h y to use fcdhcfid Pressures, as The Various useful ester base oils are disclosed in US. temperathhas q at ahhospheirlc Pressure to mmove Patents Nos. 2,499,983; 2,499,984; 2,575,195; 2,575,196; the Water formed do not iusuallv unduly degrade the 2,703,911; 2,705,724 and 2,723,286. Gene-rally, the syn- 10 P thetic base oils consist essentially of carbon, hydrogen When f h glycols With dlhaslc acids to 'P and oxygen, i.e. the essential nuclear chemical structure P l h It P t0 CODUHUC the {6360011 t is formed by these elements alone. However, these oils cohcomlthht holhhg Off of Water from h h h may be Substituted with other elements Such as halogens, ture until the polyester product has a kinematlc viscosity chlorine and fluorina some representative of about 15 to 200 centistokes at 210 F., preferably about ponents f faster lubricants are ethyl palmitae, ethyl 40 to 130cer1t1stokes. When this point has been reached, stearate, dit2-ethylhexyl) sebacate, ethylene glycol di- T p g h an be stopped, foninstance, by addlaurate, di(2-ethylhexyl) phthalate, di(1,3-methyl butyl) mg P PP alcohol to the rehchoh hhxthre, and adipate, di(2 ethy1 butyl) ,adipate 1 Drops/1) co'ntlnuinig to reflux until water ceases to be evolved. adinate. diethyl oxVlate, glycerol tri-n-octoate, di-cyclo- 2h The capplhg alcohol 15 a 10W molhchlar Weight mono [hexyl adipate, di (undecy1) sebacate tetra ethy1ene 1 alcohol of up to about carbon atoms. It is standard col-di-(2-ethylene hexoate), di-Cellosolve phthalate, butyl h when rs are made using the conventional phthauvl butyl g1yco]ate di n hexyl fumarate polymmacid catalysts such as sodium bisulfate or paratoluenedmmzyl se-bacate, and diethylene glycol bis(z n butoxy sulfonic acid, to give the esters an after-treat by washing ethyl carbonate). 2-ethylhexyl-adipate-neopentyl glycyl- F ester h a 5% aqueous KZCO3 Sohlhoh by heat; adipate-2-ethylhexyl is a representative complex ester. mg h ester 'f autoclave 15 hours at t to The es ers are manufactured. in general. by mere re- Whh 10 We1ght h of Propylene f It action of the alcoholic and acidic constituents, althou gh also ccfhvehhohal to h' the esteh to hhrahoh to Simple esters may be converted to longer chain move msoluble materials. After this the product may ponents by transesterification. The constituents, in the 30 be subjected to a reduced Pressure distillation of Stripping proportions suitable f giving the desired ester are at 100 to 200 C. to remove volatile inaterlals, such reacted preferably in the presence of a catalyst and as waterithe shlvehthhdhght h solvent or Water entraininig agent to insure maintenance The fohowlhg fixamlhes are lhchlded to further lhhs' of the liquid state during the reaction. Aromatic hydro- 7 hate the Pms'hht lhvehhoh' carbons such as xylene or toluene have proven satis- Samples 9 all esterhflsfid fiuld containing phenyl-mfactory as solvents. The choice of solvent influences hahhthylahhhe labhrhvlated PAN) or ah Nshhshhhhd the choice of temperature at which the esterifica-tion is cofhhohhd ldehhhed 1h hh' I below a Samples conducted; for instance, when toluene is used a temneratalhlhg h the adchhves were Shhlhcteh to Oxygen ture of 140 C. is recommended; with Xylene, tempera: O ahsorphoil tests at The ester Was mlres up to about 5 may be used To provide a 4 posed of a blend of 80% complex ester prepared from 1 better reaction rate an acid esterification catal st is (when "1016 heopehtyl glycol, 2 moles ofnazelalc and 2 used. Many of these catalysts are known and include, moles -oc yl alcohol and 20% duso-octyl azelate. f instance HCL 50 NaHSO, aliphatic and aro The oxygen absorption tests were conducted by passmatic sulfonic acids, phosphoric acid. hydrobrornic acid, mg a stream of oxygehat the rate of 1 chhlc h Per hour HF and dih d fl b j acicy Other catalysts are through 15 grams of the samples and noting the total thionyl chloride, boron trifluoride and silicon tetrafluotime (Tr) 1h Ihlhhtes requred to absorb 2500 Ihhhhters ride. Titanium esters also make valuable esterification of Oxygen and the Induction Perlod 1n Inlnut$$- and transesterification catalysts. The induction time is the period during which often a In a preferred reaction about 0.5 to about 1 Weight permhlOr Portion of the Oxygen is ahshrhed y fluid cent, or advantageously, 0.2 to 0.5% of the catalyst i and its end is signalled by a marked increase -l1'1 the rate used with xylene solvent at a temperature of 165 to 200 05 Oxygen p A180 noted is the VOhlme of 2 C.'Wllll6 refluxing water. The temperatures of the reabsorbed during the induction period and is identified in action must be sufficient to remove the water from the the table as Vi. esterification mass as it is formed. This temperature is The results of these tests are shown in Table I.

TABLE 1 Sample No. Additives Wt. T2 'It Vi percent 1 PAN 0.5 75.0 103 217 2 Q-aminopyridine 0.5 90.6 148 602 0.5 248 5 Benzylidene 2,2 (4-picolyl)aminc. 0.? 218 730 PAN 0.5 168 6 Benzyl dene ?,2-di-(4-picolyl)aminc O. 2 S1 0 7 2-an1'l1'nopyridine 1.0 12 234 1,060

PAW 0.5 186 1.0 271 7s2 0.5 210 1.0 210 1,150 0.5 105 10 Zanilinoquinoline 1. O 109 O 11 2, fi-di (Q-pyridylaminomethyl)4-t 1. 0 14 281 884 octylpheno]. 211 PAN 0.5 12 2,6ditQ-pyridylaminornethyh-t- 0.2 176 640 octylphcnol. 122 PAN 0.5

TABLE II.OXIDATION-CORROSION TEST DATA (347 F., 72 HRS.)

Sample No 5 12 Additives, percent:

38. 22 37. 76 0. 90 0. 43 Changes:

KV/lOO, percent 5. 23 4. cid No 0.77 0.28 Wt. change, nag/cm):

Al alloy +0. 038 +0. 007 Mg alloy 0. 046 0. 015 teeL +0. 046 0.0 Copper 0. 031 0. 015 Silver. +0. 031 +0. 007

l ylidene 2,2-di-(4pieolyl)amine. 3 2,6-di(2-pyridyl-amino-methyl) i-t-oetylphenol.

The data of Table II show that the compositions of the present invention exhibit acceptable metal corrosion characteristics and small increases in viscosity and acid number as well.

It is claimed:

1. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of an ester based fluidsoluble aromatic amine having the general formula:

wherein Q is a monovalent aromatic hydrocarbon radical of 6 to 20 carbon atoms and Q is an aromatic hydrocarbon radical of 6 to 16 carbon atoms and about 0.01 to 5% by weight of an N-substituted amino-compound represented by the general formula:

wherein X is selected from the group consisting of pyridyl and q-uinolyl radicals; R is an n-valent aromatic hydrocarbon raidcal of 6 to 24 carbon atoms, and n is 1 to 2, said amounts being suflicient to retard oxidation of said ester based fluid at 450 F. and said ester based flui'd being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

2. The composition of claim 1 wherein the aromatic amino is phenylnaphthylamine.

3. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating Viscosity, about 0.01 to 5% by Weight of an ester based fluidsoluble aromatic amine having the general formula:

carbon radical of 6 to 16 carbon atoms and about 0.01 to 8 5% by weight of an ester based fluid-soluble N-substituted aminopyridine having the structural formula:

wherein R is selected from the group consisting of hydrogen and lower alkyl and R is an aryl group of 6 to 12 carbon atoms, said amounts being suflicient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

4. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of an ester based fluidsolub'le aromatic amine having the general formula:

wherein Q is a monovalent aromatic hydrocarbon radical of 6 to 20 carbon atoms and Q is an aromatic hydrocarbon radical of 6to 16 carbon atoms and about 0.01 to 5% by weight of an ester based fluid-soluble N-su-bstituted aminoq-uinoline compound having the structural formula:

R NHR,

wherein R is hydrogen and R is an aryl group of 6 to 12 carbon atoms and R and NHR are on diflerent carbon atoms of the positions 2 to 8, said amounts being sufficient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

5. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of an ester based fluidsoluble aromatic amine having the general formula:

wherein Q is a non-'olefinic, non-acetylenic monovalent hydrocarbon of 1 to 20 carbon atoms and Q is an aromatic hydrocarbon radical of 6 to 16 carbon atoms and about 0.01 to 5% by weight of an ester based fluid-soluble aromatic amine having the general formula:

wherein R is an alkyl group of 1 to 12 carbon atoms and R is an aryl group of 6 to 12 carbon atoms, said amounts being suflicient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

6. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of an ester based fluidsoluble aromatic amine having the general formula:

wherein Q is a non-olefinic, non-acetylenic monovalent hydrocarbon of 1 to 20 carbon atoms and Q is an aromatic hydrocarbon radical of 6 to 16 carbon atoms and 9 about 0.01 to by weight of an ester based fluid-soluble aromatic amine having the general formula:

wherein R is hydrogen; R is a divalent alkyl radical of 1 to 4 carbon atoms and R is an alkyl group of 1 to 8 carbon atoms, said amounts being sufiicient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

7. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of phenylnaphthylamine and about 0.01 to 5% by weight of Z-anilinoquinoline, said amounts being suflicient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

8. A lubr cating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of phenylnaphthylamine and about 0.01 to 5% by weight of 2-ani'linopyridine, said amounts being sufficient to retard oxidation of said ester base fluid at 450 F. and said ester base fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

9. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of phenylnaphthylamine and about 0.01 to 5% by weight of 2-(N-benzy1amino)4- picoline, said amounts being suflicient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxylic acid of 4 to 12 carbon atoms.

10. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of phenylna'phthylamine and about 0.01 to 5% by weight of benzylidene-2,2-di(4- picoly1)amine, said amounts being s-uificient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane carboxy lic acid of 4 to 12 carbon atoms.

11. A lubricating oil composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight of phenylnaphthylamine and about 0.01 to 5% by weight of 2,6-di(2-pyridylaminome-thyl)4-tertiary octyl phenol, said amounts being suflicient to retard oxidation of said ester based fluid at 450 F. and said ester based fluid being an ester of an alkanol of 4 to 12 carbon atoms and an alkane canboxylic acid of 4 to 12 carbon atoms.

References Cited by the Examiner UNITED STATES PATENTS 2,136,788 11/1938 Fairlie 252- 2,198,961 4/1940 Dietrich 252-50 X 2,290,032 7/1942 Burk 252-50 X 2,318,196 5/1943 C'henicek 4463 2,336,006 12/1943 Fuller 252-51.5 2,361,339 10/1944 White et a1 25251.5 2,363,778 11/1944 Pedersen 44-63 2,459,112 1/ 1949 Oberright H 252--51.5 2,637,636 5/1953 Walters 4463 2,933,379 4/1960 Fields 4463 3,043,783 7/1962 Hatcher et a1 252-51.5 X 3,093,585 6/1963 LOW et a1 25251.5 X 3,121,691 2/1964 Eickemeyer 252--51.5

DANIEL E. WYMAN, Primary Examiner.

P. P. GARVIN, Assistant Examiner. 

1. A LUBRICATING OIL COMPOSITION CONSISTING ESSENTIALLY OF AN ESTER BASED SYNTHETIC FLUID OF LUBRICATING VISCOSITY, ABOUT 0.01 TO 5% BY WEIGHT OF AN ESTER BASED FLUIDSOLUBLE AROMATIC AMINE HAVING THE GENERAL FORMULA: Q''-NH-Q WHEREIN Q IS A MONOVALENT AROMATIC HYDROCARBON RADICAL OF 6 TO 20 CARBON ATOMS AND Q'' IS AN AROMATIC HYDROCARBON RADICAL OF 6 TO 16 CARBON ATOMS AND ABOUT 0.01 TO 5% BY WEIGHT OF AN N-SUBSTITUTED AMINO-COMPOUND REPRESENTED BY THE GENERAL FORMULA: R(-NH-X)N WHEREIN X IS SELECTED FROM THE GROUP CONSISTING OF PYRIDYL AND QUNOLYL RADICALS; R IS AN N-VALENT AROMATIC HYDROCARBON RADICAL TO 6 TO 24 CARBON ATOMS, AND N IS 1 TO 2, SAID AMOUNTS BEING SUFFICIENT TO RETARD OXIDATION OF SAID ESTER BASED FLUID AT 450*F. AND SAID ESTER BASED FLUID BEING AN ESTER OF AN ALKANOL OF 4 TO 12 CARBON ATOMS AND AN ALKANE CARBOXYLIC ACID OF 4 TO 12 CARBON ATOMS. 